(a) Field of the Invention
The present invention relates to a copolymer including an alkylene carbonate and a method of preparing the same, and specifically, to a copolymer including an alkylene carbonate using carbon dioxide and a method of preparing a copolymer including the alkylene carbonate that has excellent biodegradable properties.
(b) Description of the Related Arts
The development of industries in countries all over the world and the increase in population have increasingly destroyed the natural environment, and as industries in all fields develop, consumption of fossil fuels has increased drastically, causing a big increase in the amount of emitted air pollutants. In particular, among these air pollutants, gases causing the greenhouse effect have increased drastically, causing a big problem in climate changes all over the world. Carbon dioxide has received attention as a major cause of the greenhouse effect. Recently, proposals restricting the emission of carbon dioxide throughout the world have been sought, at the center of which lies the U.N. Framework Convention on Climate Change. A new solution for reducing the emission of carbon dioxide is to utilize it as a raw material for producing polymer materials. This can contribute greatly to humanity and the protection of the earth""s environment.
Furthermore, polymer materials including plastics have contributed greatly to convenience in our day-to-day lives and the development of various modern industries, but the polymer materials have caused environmental pollution as their use increases day by day followed by a corresponding increase in the waste polymer materials after their use. Therefore, increasing attention has been given to polymer materials that can be hydrolyzed or biodegraded by microorganisms to protect the natural environment.
An object of the present invention is to provide a method of preparing a copolymer including an alkylene carbonate using carbon dioxide, which is an air pollutant source.
Another object of the present invention is to provide a copolymer including an alkylene carbonate that has excellent biodegradable properties.
In order to achieve the above objects, the present invention provides a method of preparing a copolymer including an alkylene carbonate, including terpolymerization of delta-valerolactone or lactide represented by Formula 3, carbon dioxide, and alkylene oxide, in the presence of a catalyst. In the above method, when lactide is used, poly(alkylene carbonate lactide) of Formula 1 is prepared, and alternatively, when delta-valerolactone is used, poly(alkylene carbonate-delta-valerolactone) is prepared. 
(wherein, xe2x80x94Oxe2x80x94Axe2x80x94 is an opened alkylene oxide structure, the alkylene oxide being selected from the group consisting of ethylene oxide, propylene oxide, 1-butene oxide, 2-butene oxide, 1,1-dimethylethylene oxide, cyclopentene oxide, cyclohexene oxide, 1-phenylethylene oxide, 1-vinylethylene oxide, and 1-trifluoromethylethylene oxide; and,
x and y are independently an integer being equal to or less than 2,000, n is an integer, and n=(z-x-y), wherein z is an integer being equal to or less than 20,000.)
Alternatively, the present invention provides a poly(alkylene carbonate-lactide) copolymer represented by Formula 1, or a poly(alkylene carbonate-delta-valerolactone) copolymer represented by Formula 2.
The present invention relates to a method of preparing a copolymer including an alkylene carbonate that has excellent biodegradable properties using carbon dioxide which is a main component of greenhouse gases that cause the greenhouse effect. The copolymer of the present invention is preferably a poly(alkylene carbonate-lactide) or a poly(alkylene carbonate-delta-valerolactone).
The method of preparation of the present invention includes terpolymerization of delta-valerolactone or lactide represented by Formula 3, alkylene dioxide, and carbon dioxide, in the presence of a catalyst. 
The alkylene oxides usable in the present invention are compounds of Formula 4, which are selected from the group consisting of ethylene oxide, propylene oxide, 1-butene oxide, 2-butene oxide, 1,1-dimethylethylene oxide, cyclopentene oxide, cyclohexene oxide, 1-phenylethylene oxide, 1-vinylethylene oxide, and 1-trifluoromethylethylene oxide. 
In the method of the present invention, the terpolymerization process of carbon dioxide, the alkylene oxide (xe2x80x94Oxe2x80x94A-ring), and lactide is shown in Reaction Formula 1. 
Hereinafter, lactide or delta-valerolactone is defined as xe2x80x9cmonomer 1xe2x80x9d.
In the detailed method of the present invention, alkylene oxide and monomer 1 are first mixed in a molar ratio of 99.99:0.01 to 0.01:99.99, and a catalyst is then added to the mixture. This process is suitably carried out under a nitrogen atmosphere and generally in a pressurized reactor, in order to facilitate polymerization.
The catalyst is added in an amount of 0.1 to 20.0 wt % based on the total amount of monomer 1 and alkylene oxide; and the catalyst is zinc glutaric acid, preferably vacuum-dried zinc glutaric acid, which has excellent catalytic activity.
The zinc glutaric acid catalyst used in the present invention is prepared as follows. Zinc oxide or zinc hydroxide, and glutaric acid, are used in the same equivalent and toluene is used as a solvent. The mixture is vigorously stirred, it is reacted at 55xc2x0 C. for 2 hours, and then for 4 hours under reflux, to prepare zinc glutaric acid. After the reaction, the solid zinc glutaric acid product is filtered while washing with acetone, and then dried in a vacuum-drying oven at 50 to 150xc2x0 C. for one day.
Carbon dioxide is then injected into the mixture at a pressure of 50 to 1000 psi, and terpolymerization is carried out for 20 to 80 hours at 0 to 100xc2x0 C. When the carbon dioxide injection pressure is lower than 50 psi, the concentration of carbon dioxide in a reactor is low so that it results in a low reaction yield during the polymer synthesis. Alternatively, when the carbon dioxide injection pressure is higher than 1000 psi, there is a danger of accidents caused by high pressure and there is a need to have a high-pressure reactor that is specially prepared for tolerating high pressures. When the reaction temperature is lower than 0xc2x0 C., it takes a long time to carry out the reaction, and when the temperature is higher than 100xc2x0 C., by-products other than polymers are produced. When a pressurized reactor is used, carbon dioxide is injected after the pressurized reactor is covered with a lid in order to facilitate polymerization. Since the melting point of lactide is 116 to 119xc2x0 C., lactide is solid below 100xc2x0 C., and therefore, when lactide is used as a monomer 1 and an amount of solid lactide is more than a 50 molar ratio, organic solvents such as 1,4-dioxane, toluene, benzene, methylene chloride, or cyclohexane are preferably used. Regarding delta-valerolactone, since it is liquid below 100xc2x0 C., there is no problem mixing the reactants irrespective of their amount. Therefore, there is no need to use the above organic solvent, but it can be used if needed.
By the above process, a poly(alkylene carbonate-lactide) copolymer of Formula 1 or a poly(alkylene carbonate-delta-valerolactone) copolymer of Formula 2 is produced. 
(wherein, xe2x80x94Oxe2x80x94Axe2x80x94 is an opened alkylene oxide structure, the alkylene oxide being selected from the group consisting of ethylene oxide, propylene oxide, 1-butene oxide, 2-butene oxide, 1,1-dimethylethylene oxide, cyclopentene oxide, cyclohexene oxide, 1-phenylethylene oxide, 1-vinylethylene oxide, and 1-trifluoromethylethylene oxide; and,
x and y are independently an integer being equal to or less than 2,000, n is an integer, and n=(z-x-y), wherein z is an integer being equal to or less than 20,000.)
After the completion of the reaction, the copolymer produced is diluted with organic solvent such as carbon dichloride and washed with diluted hydrochloric acid. Then, the washed copolymer is washed again with distilled water and precipitated with methanol to separate the copolymer. The obtained copolymer is dried at ambient temperature in a vacuum-drying oven. Additionally, if needed, a removing process of the remaining catalyst in the produced copolymer can be further carried out.
When lactide is used as a monomer 1, the produced poly(alkylene carbonate-lactide) copolymer has a molecular weight of 1,000 to 2,000,000, and it is preferably poly(propylene carbonate-lactide) of which the molecular weight is 1,000 to 2,000,000, poly(ethylene carbonate-lactide) of which the molecular weight is 1,000 to 2,000,000, or poly(cyclohexene carbonate-lactide) of which molecular weight is 1,000 to 2,000,000. In addition, when delta-valerolactone is used as a monomer 1, the produced poly(alkylene carbonate-delta-valerolactone) copolymer has a weight average molecular weight of 1,000 to 2,000,000, and it is preferably poly(propylene carbonate-delta-valerolactone) of which the weight average molecular weight is 1,000 to 2,000,000, poly(ethylene carbonate-delta-valerolactone) of which the weight average molecular weight is 1,000 to 2,000,000, or poly(cyclohexene carbonate-delta-valerolactone) of which the weight average molecular weight is 1,000 to 2,000,000.
The method of the present invention uses carbon dioxide as a main ingredient, which is a main cause of air pollution and the greenhouse effect, and alkylene oxide which is relatively cheap, and lactide or delta-valerolactone which have biodegradable properties and prepare a poly(alkylene carbonate-lactide) copolymer or a poly(alkylene carbonate-delta-valerolactone) copolymer. Thus, the present invention produces new polymer materials using carbon dioxide fixation so that it contributes to suppression of air pollution and the climate change phenomenon by carbon dioxide because it reduces an amount of carbon dioxide through recycling thereof. Since a poly(alkylene carbonate-lactide) copolymer and a poly(alkylene carbonate-delta-valerolactone) copolymer prepared by the method of the present invention have excellent hydrolysis and biodegradable properties, they can be used as general polymer materials that do not cause environmental pollution as well as for medical polymer materials.
Hereinafter, preferred examples are provided to assist the understanding of the present invention. These following examples, however, are only for the purpose of facilitating understanding of the invention and should not be construed to be limiting in any sense.